The operating property of the permanent magnet motor is determined by the magnetization property of the permanent magnet within the motor. A magnetic analyzer with a Hall sensor is usually used to check the qualified magnetization of the permanent magnet. Please refer to FIG. 1, which is a drawing showing that the magnetic analyzer is used to check the permanent magnet of the motor in the prior art. As shown in FIG. 1, the magnetic analyzer 11 including the probe 111 and Hall sensor 112 is used to check the permanent magnet. After the probe 111 goes round the rotor 12, the magnetic density of the permanent magnet's surface could be obtained.
Nevertheless, such a conventional equipment has at least the following disadvantages. (1) It is necessary to adjust the relative positions between the permanent magnet and probe many times during the checking process, and it takes lots of time. (2) The probe is relatively fragile and thus unsuitable for use on the production line. (3) The probe has a volume. When the probe is used to check a tiny motor, the position errors resulting from the volume of the probe would cause an unacceptable checking error to the checking result. (4) It is necessary to remove the core of the stator before the checking. Therefore, the measured result is not the real air-gap magnetic density distribution of the motor under the normal operations. Accordingly, it is unable to perform a precise analysis to the operation property of the motor based on the measured result.
In addition, the quality of the permanent magnet within a permanent magnet motor could be also determined by the back electromotive force of the winding. An advantage of such testing method is that the measured result could faithfully reflect the contribution of the permanent magnet to the magnetic path and the magnetic field of the motor during the operation of the motor. Therefore, it is possible to precisely analyze the operation property of the electric machinery based on the measure result. There exists no position issue between the sensor and the permanent magnet of the rotor. The testing result is extremely precise. Nevertheless, such testing method has two demands: (1) the rotor must be rotating; and (2) no driving current flows in the motor winding.
As above mentioned, a driving equipment is required for driving the rotor of the motor to be test the voltage of the winding of the stator i.e. the back electromotive force is obtained when the rotor driven by driving equipment. Please refer to FIG. 2, which shows the drawing that a driving equipment is applied for driving the rotor of the motor to be tested in order to measure the back electromotive force of the motor in the prior art. As shown in FIG. 2, the driving equipment includes the driving device 22 electrically connected to the driving circuit 21 to drive the rotor 23 via coupling portion 25, and then the back electromotive force of the motor is obtained by the detector 24. Nevertheless, the existence of the driving device 22 makes the testing system complex. In addition, it further takes lots of time to match the driving rotor of the driving device 22 with the rotor need to be tested (referring to the coupling portion 25 in FIG. 2). Therefore, the mentioned testing method is not suitable for use in the mass production either.
As above-mentioned, in order to optimize the method for testing the back electromotive force of the motor in the prior art and remove the driving device 22 in FIG. 2, a new method and circuit for testing the motor is necessary. An object of the present application is to provide a method and circuit with the higher preciseness, less checking time, more convenience and simpleness based on the measuring and analysis of the back electromotive force of the tested motor.